D:\archiwum\vol19fasc4\vol19fasc4.vp

Arch. Pol. Fish. (2011) 19: 259-265DOI 10.2478/v10086-011-0032-5
RESEARCH ARTICLEMarking and return method for evaluating the effects of stocking larvalvendace, Coregonus albula (L.), into Lake Wigry in 2000-2001Received – 12 April 2011/Accepted – 10 October 2011. Published online: 30 December 2011; Inland Fisheries Institute in Olsztyn, PolandPawe³ Poczyczyñski, Krzysztof Koz³owski, Jacek Koz³owski, Andrzej MartyniakAbstract. In 2000 and 2001, larval vendace, CoregonusIntroductionalbula (L.), were marked and released into Lake Wigry. Thelarvae were immersed in alizarin red S. Of the 19.2 million
Marking and return studies are one of the best methods
vendace larvae released in 2000, 2 million were marked(10.4% of the overall number of fish released), and in 2001 of
for investigating various aspects of the biology of many
the 18.8 million fish released, 7 million were marked (47.8%).
fish species. They are particularly useful for identifying
In subsequent years, otoliths were excised from caught
population dynamics, migration research, and deter-
vendace and the number of them with alizarin marks was
mining stocking effectiveness (Everhart et al. 1975,
determined. It was assumed that all unmarked specimens
Mills and Beamish 1980, Babaluk and Cambell 1987,
came equally from natural spawning and stocking assuming
Hilborn et al. 1990, Meunier 1994, Secor and Houde
that survival is equal in both forms of recruitment. It wasconfirmed that 82.4% of the vendace caught from the 2000
1995). Techniques for marking fish have improved
generation originated from stocking, while this figure was
vastly in the past fifty years. Earlier methods (e.g., clip-
64.2% of all specimens caught from the 2001 generation.
ping fins, freezing, attaching external tags) are increas-
Lake Wigry hosts the most abundant vendace population in
ingly being replaced by more modern methods such as
Poland, and this stock spawns on a massive scale annually.
attaching PIT or microtags with binary or alphanumeric
Even so, the study described herein provides evidence of just
codes. However, these methods cannot be used to mark
how important systematic stocking is to the maintenance ofthe vendace population in this lake.
larval fish because of their small sizes. Evaluating theeffects of stocking larvae was basically impossible until
Keywords: vendace, otoliths, alizarin red S, marking and
a method was developed for marking juvenile fish on
return method, marking coefficient, stocking
a mass scale using, among other methods, chemicalagents or thermal shock. Marking is the only methodthat provides reliable data on the success of reinforcingnatural reproduction through stocking in a given basin(Koz³owski 2007). Intense research into marking fishusing chemicals was the begun in the 1960s. Two dis-tinctively different methods were developed. One ofthese methods uses strontium chloride. As strontium is
P. Poczyczyñski [+], K. Koz³owski, J. Koz³owski, A. Martyniak
a calcium analogue, it is built into the bone structures
Department of Fish Biology and Pisciculture
of fish (Ophell and Judd 1968, Bagenal et al. 1973).
Faculty of Environmental Sciences and Fisheries
Otoliths are analyzed using atomic mass spectrometry
University of Warmia and MazuryOczapowskiego 5, 10-719 Olsztyn, Poland
(AMS) and atomic absorption spectrometry (AAS). The
Tel. +48 89 523 32 62, e-mail: [email protected]
second, far more popular marking method is to use
fluorochromes, which form chelate complexes with cal-
on March 10, 2000. Alizarin red S, was used to mark
cium ions that are built into skeletal and otolith struc-
two-day-old larvae. The fish were immersed in an
tures. Markings are visible under ultraviolet light since
alizarin solution (Tsukamoto 1988, Nagiêæ et al.
the calcium-fluorochrome complexes emit fluorescent
1995). The water supply was shut off to a tank with
light (Beverander and Goss 1962, Monaghan 1993).
a volume of 800 dm3 in which there were 2 million
The abundance of the family Coregonidae in Po-
larval vendace; then 170 g of alizarin was dissolved
land has been dependent on stocking for many years,
in the water (concentration 200 ppm). The water
and until a certain time, the number of lakes in which
temperature was 5.3°C. During marking, which
these fish occurred increased as a result of the imple-
lasted for 4 hours, the amount of dissolved oxygen in
mentation of various management strategies. In the
the water was monitored systematically. After 2
1958-1969 period, the number of coregonid lakes
hours, the oxygen concentration decreased to 43.8%,
reached 420, which comprised 62% of the total sur-
which is why the water in the tank was supplemented
face area of Polish lakes. Later, disadvantageous en-
to a volume of about 1000 dm3. After four hours of
vironmental changes, decreased stocking intensity,
immersion, water flow was restored in the tank. No
changes in management strategies, and intense fish-
increased mortality was noted during marking. It can
eries led to smaller Coregonidae populations, and
take up to 14 days for alizarin to chelate with calcium
even their extinction in some basins (Bniñska 1998,
ions. To verify the effectiveness of the marking and
Wo³os 1998a, 1998b, Wo³os and Mickiewicz 1998,
determine its quality, 100 vendace larvae were
reared for two weeks in an aquarium. Then otolithswere excised from 36 fish, mounted with Entellan
Lake Wigry, with a surface area of 2186.7 ha, is
Neu, and viewed under a Nikon OPTIPHOT 2 in
the tenth largest lake in Poland. It is of a mixed
UV-B at a magnification of 800x. The markings were
trough–morena origin, with a highly varied shoreline
legible on all of the otoliths viewed. A second mark-
and bottom topography. There are 18 islands in the
ing was performed in the same hatchery on March 19
lake with a total surface area of 68.4 ha. The maxi-
and 20, 2001 when 9 million vendace larvae were
mum depth is 73 m, which makes Lake Wigry the
marked. Because of the large number of larvae and
fifth deepest lake in Poland. The population of ven-
the oxygen deficit in the water that occurred in the
dace, Coregonus albula (L.), in Lake Wigry is proba-bly the most abundant in Poland. Its biomass is
previous year, this time marking was performed in
estimated at 222 kg ha-1 (Œwierzowski 1999). Cur-
two rounds and in a greater number of tanks. On the
rently, annual catches range from 10 to 20 tons. The
first day, marking was conducted in two tanks, one
aim of the present study was to evaluate the effects of
with a volume of 650 dm3 and the second with a vol-
stocking Lake Wigry in 2000 and 2001 with marked
ume of 450 dm3. The water temperature was 5.9°C.
larvae using the stocking-return method. In order to
Again, alizarin S was used at a concentration of 225
perform calculations, the marking coefficient (MC),
ppm. Marking was completed after three hours. The
which is described in the Materials and methods sec-
oxygen content during the procedure did not de-
crease below 9.0 mg dm-3, which was about 74% sat-uration. On the second day, marking was performedin one tank with a volume of 650 dm3 and in threewith a volume of 450 dm3. The water temperature
Materials and Methods
was 6.3°C. Immersion time in the alizarin solution ata concentration of 200 ppm was three hours. The
The stocking material originated from vendace
concentration of oxygen in the water remained above
spawners caught in Lake Wigry. The eggs were incu-
71%. After the conclusion of marking, 100 vendace
bated at a hatchery (Wigierski National Park, Po-
larvae from each tank were held for rearing. After 16
land). The first marking of larvae vendace was done
days the otoliths were excised and examined using
Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).
the same procedures applied to the fish in 2000.
required introducing the marking coefficient param-
Brightly shiny marks were confirmed in all 124 of the
eter (P), which expresses the ratio of fish marked to
otoliths examined. In 2000, Lake Wigry was stocked
all vendace produced through artificial breeding and
with 19.2 million vendace larvae, of which 10.4%
released into a given lake. In 2000 this parameter
had been marked. In the following year, 18.8 million
was 9.61 (100%:10.4%), while in 2001 it was 2.09
larval vendace were released, of which 47.8% were
Assuming that mortality in marked and un-
The material analyzed came from commercial
marked hatch is equal (Czerkies 1998), it was possi-
and experimental catches conducted in 2002-2005
ble to calculate the percentage of catches that
originated from stocking. To do this, the marking co-
efficient was multiplied by the share of marked fish
Number of otoliths obtained from the 2000 and 2001
Of the total number of fish stocked into Lake Wigryin 2000, otoliths from 312 specimens were read,
The otoliths examined came from fish of the
while in 2001, the otoliths from 346 vendace speci-
2000 and 2001 generations. The age of the fish was
determined based on scale readings. The otoliths
chosen for examination were mounted on glass slides
Number of otoliths analyzed microscopically from vendace
with Entellan Neu. After a week they were, polished
from the 2000 and 2001 generations by age groups
with fine-grade 1000 and 1200 waterproof sandpa-per. One-sided polishing was applied to the otoliths
of young fish aged 1+ to 3+. The otoliths of older fish
were polished on both sides. During polishing, the
otoliths were examined under a light microscope at
a magnification of 400x. Polishing was stopped oncethe center of the otolith, where the mark had been re-
The best quality marks were noted in fish aged
corded, was exposed. Processing the material re-
1+. In older fish, while the marks on the otoliths were
quired precision and great care since the otoliths are
less visible, they were still distinct enough to exclude
fragile and are easily damaged. Additionally, the
identification error. Among the 312 otoliths exam-
otolith center is convex, and excessive polishing can
ined from the 2000 generation, 27 (8.6%) had dis-
cause it to collapse. During polishing, 112 otoliths
tinct alizarin marks, with the most (22) noted in the
were damaged, including all of those from fish aged
2+ age group. This comprised 9% of the otoliths ana-
5+, 15 from fish aged 4+, 12 from fish aged 3+, and
lyzed in this age group. Among the fish aged 1+ and
72 from fish aged 2+. Of the remaining 734 otoliths,
2+ examined, marked otoliths were noted in 2 and 3
76 were illegible, thus 658 otoliths were used to ana-
fish or in 1.8 and 5.8%, respectively (Table 2). Of the
lyze the alizarin marks in legible otolith centers. The
346 otoliths examined from the 2001 generation,
prepared materials were examined under a Nikon
109 alizarin marks were confirmed (31.5%). Simi-
OPTIPHOT 2 microscope in UV-B at a magnification
larly, the most marks were noted in fish aged 2+ (85
individuals, which was 37.9% of the whole sample).
Estimating the effects of stocking during which
The number of marked otoliths from fish aged 1+
only a portion of the material released was marked
and 3+ was 22 and 2, which was 30.8 and 16.7%,
Koz³owski 2007), which is nearly twice the average
amount of stocking material released other Polish
lakes at 3860 larvae per ha-1 (Wo³os 1998b). Larval
vendace were released into Lake Wigry systemati-
cally, and the stocking frequency coefficient was 1,
which indicates annual stocking. According to data
published by Leopold (1998a), coefficient values
above 0.7 were noted in only 2.6% of the lakes ana-
The statistical analysis of vendace stocking and
catches in Lake Wigry did not indicate significant de-
Figure 1. Share (%) marked larval vendace in the entire sample
pendencies between these variables (Koz³owski
2007). In this study, the analyses of correlations be-tween stocking and catches one and two years follow-
respectively, of the analyzed individuals in these age
ing stocking did not exhibit any significant statistical
correlations between these variables. No statistically
The proportions between the share of marked
significant dependencies in the analysis of correla-
larvae released into the lake and the share of marked
tions between stocking, taking into consideration the
otoliths in the material collected were similar. In the
two and three year moving variables, and catches
generation from 2000, the share of marked larvae
were noted. While the lack of statistically significant
was 10.4%, and the share of marked otoliths was
dependencies between stocking and catches of ven-
8.6%. Based on the proportion of marked fish to the
dace have been confirmed in many lakes, this does
number of fish caught, 82.4% of the vendace caught
not provide evidence that stocking is ineffective. The
came from stocking. In the 2001 generation, marked
lack of correlations can be explained by the greatvariability in the amounts of stocking material re-
larvae comprised 47.8%, and the share of marked
leased, breaks in stocking, the application of various
otoliths was 31.5%. The share of vendace from the
kinds of stocking materials, the success of natural
spawning, and, as is the case in Lake Wigry, low lev-els of exploitation (Koz³owski 2007). According toa study by Leopold (1998b) conducted on 60 ven-
Discussion
dace lakes in Poland, the mean number of larvae re-leased that corresponded to 1 kg of commercial
Stocking Polish lakes with coregonids has been the
vendace ranged from 720 to 2,138 individuals de-
focus of many studies of the effectiveness of this mea-
pending on the basin. During this study period, Lake
sure as well as the general principles for the manage-
Wigry, with 1,273 larvae released per kg of vendace
ment of these species (Falkowski 1998). In Poland,
caught, was classified as a lake with medium stock-
the most common type of vendace stocking material
is freshly-hatched larvae. The share of vendace sum-
Applying fluorescent markers using the immer-
mer fry in stocking is slight and, according to Wo³os
sion technique is a relatively simple procedure that is
(1998a) it comprises barely 0.4% of all the stocking
possible to perform in virtually any hatchery. Its ad-
material released into 123 basins that he analyzed.
vantages include the low cost and the possibility of
Lake Wigry has been and continues to be stocked ex-
marking large numbers of fish in early developmen-
clusively with larvae. The average number of larvae
tal stages. While the marking procedure is performed
released into this lake in the 1977-2004 period was
without any great difficulty, reading fish otoliths re-
15.8 million larvae annually (7241 larvae ha-1;
quires sacrificing the fish and specialist equipment
Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).
such as a fluorescent microscope. Preparing the oto-
was stocked with two types of vendace stocking mate-
liths is also a labor-intensive task. Additionally, oto-
rial: hatch (300,000 individuals) and summer fry
liths are often damaged while being polished, which
(15,000 individuals). The larvae were marked with
excludes them from further analysis. While prepar-
alizarin, while the summer fry were marked with tetra-
ing 423 otoliths for analysis, Czerkies (1997, 1998)
cycline. Of the 170 fish caught, the author confirmed
discarded 233 as damaged ones with illegible cen-
alizarin marks in 4.5% of the individuals, while no
ters; this comprised more than 50% of the material
marks were noted in the other individuals, which was
that had been collected. The number of damaged
explained by the strong autofluorescent, amphoric
otoliths in the current study was significantly lower;
otolith centers. However, these did fish exhibit daily
because the likelihood that the otolith would be dam-
increment patterns on their otoliths that are typical of
aged was high, the second otolith was always col-
stocking and which indicated that they originated
In experiments with marking fish later released
Stocking larval vendace marked with alizarin red
into open basins, an important issue is the perma-
S into Lake Werbellin (Germany) showed how effec-
nence of the markings. The results of the current study
tive natural spawning is there (Eckmann et al. 1998).
indicate that alizarin marks remain visible in fish oto-
Among the 1072 individuals examined, only 1.3% of
liths for many years. Tsukamoto (1995) observed in
the fish had marked otoliths. In the studies in Lake
Pagrus major (Temminck and Schlegel) marks five
Wigry indicated quite the opposite situation. The
years after marking, while in grayling, Thymallus
share of marked fish was higher at 8.6% in the 2000
thymallus (L.), marks were confirmed to be at least
generation and 31.5% in the 2001 generation, which,
two years old, and brown trout, Salmo trutta L., re-
when recalculated, indicated a high share of fish
tained otolith marks for three years (Nagiêæ et al.1995). In the case of vendace from lake Wigry, otolith
from stocking in the catches at 82.4% and 64.2%.
marks were noted in fish aged 3+, but it is plausible
The results of the study described above clearly
that the marks remain visible for at least four years.
confirm the view that the occurrence of vendace in
Studies conducted to date on fish markings indi-
Polish lakes is mainly because of stocking programs.
cate that as time passes the marks in a certain num-
Even the exceptionally abundant population of this
ber of fish fade. According to Muth and Bestegen
species in Lake Wigry, despite its effective natural re-
(1991) this phenomenon occurs in the youngest fish
production, is supported largely by stocking pro-
and is linked to ultraviolet solar radiation. However,
grams. It is plausible that if stocking were
Eckmann et al. (1996), in a study of larval vendace
discontinued, vendace would disappear from this
marked with alizarin did not report the subsequent
loss of marks, and in a control group of vendace heldfor a year, all of the fish retained markings.
The technique developed in Poland for marking
References
larvae with fluorochromes can be applied to many dif-ferent fish species: whitefish; vendace; grayling; pike,
Babaluk J.A., Cambell J.S. 1987 – Preliminary results of tet-
Esox lucius, L.; rainbow trout, Onchorhynchus mykiss
racycline labelling for validating annual growth incre-
ments in opercula of walleyes – N. Am. J. Fish. Manage.
pikeperch, Sander lucioperca (L.); common bream,
Abramis brama (L.); Wels catfish, Silurus glanis L.
Bagenal T.B., Mackereth F.J.H., Heron J. 1973 – The distinc-
tion between brown trout and sea trout by the strontium
Studies of the effects of stocking have been performed
content of their scales – J. Fish Biol. 5: 555-557.
with the first four species listed (Goryczko et al. 1994,
Bevelander G., Goss R.J. 1962 – Influence of tetracycline on
1998, Nagiêæ et al. 1995, 1998). Czerkies (1998) con-
calcification in normal and regenerating teleost scales –
ducted an experiment in which Lake Garbaœ Du¿y
Bniñska M. 1998 – Coregonid management and environmen-
Meunier F.J. 1994 – Données sur la croissance de l’anguille
tal quality – In: Coregonid management. Conditions and
(Anguilla anguilla L.) dans le cours moyen du Rhin,
effectiveness (Eds) A. Wo³os, M. Bniñska, Wyd. IRS,
region Alsacienne – Bull. Fr. Pêche Piscic. 335: 133-144.
Mills K.H., Beamish R.J. 1980 – Comparison of fin - ray and
Czerkies P. 1997 – Comparing effects of stocking Lake Garbaœ
scale age determinations for lake whitefish (Coregonus
Du¿y with vendace hatch and fry – In: Proc. II Conference
clupeaformis) and their implications to estimates of
for Lake Fisheries. Significance and management, Wyd.
growth and annual survival – Can. J. Fish. Aquat. Sci. 37:
Czerkies P. 1998 – Comparing effects of stocking Lake Garbaœ
Monaghan J.P. 1993 – Comparison of calcein and tetracycline
Du¿y with vendace hatch and fry – In: Coregonid man-
as chemical markers in summer flounder – Trans. Am.
agement. Conditions and effectiveness (Eds) A. Wo³os,
M. Bniñska, Wyd. IRS, Olsztyn: 81-87 (in Polish).
Muth R.T., Bestgen K.R. 1991 – Effects of sunlight on tetracy-
Eckmann R., Czerkies P., Helms C., Kleibs K. 1998 – Evalu-
cline – Trans. Am. Fish. Soc. 113: 370-373.
ating the effectiveness of stocking vendace (Coregonus
Nagiêæ M., Czerkies P., Goryczko K., Witkowski A.,
albula (L.)) eleutheroembryos by alizarin marking of oto-
Murawska E. 1995 – Mass - marking of grayling,
liths – Arch. Hydrobiol., Spec. Issues Advanc. Limnol.Thymalus thymalus (L.), larvae by fluorochrome tagging
of otholiths – Fish. Manage. Ecol. 2: 185-195.
Everhart W.H., Eipper A.W., Youngs W.D. 1975 – Fish mark-
Ophell I.L., Judd J.M. 1968 – Marking fish with stable stron-
ing – In: Principles of Fishery Science (Eds) W.H.,
tium – J. Fish. Res. Bd. Can. 25: 1333-1337.
Everhart, W.D. Young, Cornell University Press, Ithaca,
Secor D.H., Houde E.D. 1995 – Larval mark - release experi-
ments: potential for research on dynamics and recruit-
Falkowski S. 1998 – Effectiveness of whitefish (Coregonus
ment in fish stocks – In: Recent developments in fish
lavaretus L.) management in lakes with the highest yields
otolith research (Eds) D.H. Secor, J.M. Dean and S.E.
of this fish in Poland – Arch. Pol. Fish. 6: 361-379.
Campana, Univ. South Carolina Press: 423-444.
Goryczko K., Kowalewski M., Czerkies P., Witkowski A. 1994
Œwierzowski A. 1999 – Locating and estimating stocks of
– Evaluation of the effectiveness of stocking grayling
pelagic fish using acoustic catch methods in selected
hatch in streams inhabited by natural populations of this
lakes in Wigry National Park – In: Functioning and pro-
species – Komun. Ryb. 5: 12-13 (in Polish).
tection of aquatic ecosystems in protected areas (Eds) B.
Goryczko K., Nagiêæ M., Witkowski A., Murawska E. 1998 –
Zdanowski, M. Kamiñski, A. Martyniak, Wyd. IRS,
Stocking Pomeranian rivers with grayling, Thymallusthymallus (L.), summer fry based on the example of the
Tsukamoto K. 1988 – Otolith tagging of ayu embryo with fluo-
Radunia – Rocz. Nauk. PZW 11: 81-85 (in Polish).
rescent substances – Nippon Suisan Gakk. 54: 1289-
Hilborn R., Walters C.J., Jester D.B. 1990 – Value of fish
marking in fisheries management – Am. Fish. Soc. Symp.
Tsukamoto K. 1995 – Use of otolith - tagging in a stock
enhanecement program for masu salmon (Oncorhynchus
Koz³owski K. 2007 – Characteristics of vendace (Coregonusmasou) in the Kaji River, Japan – In: Recent develop-
albula L.) populations from Lake Wigry and selected
ments in fish otolith reserch (Eds) D.H. Secor, J.M. Dean,
issues in managing this species – Department of Fish
S.E. Campana, Univ. South Carolina Press: 403-422.
Biology and Culture, UWM Olsztyn, PhD Thesis (in Pol-
Turkowski K. 2002 – Economic conditions and the effective-
ness of stocking lakes with coregonid fishes – Rozprawy
Leopold M. 1998a – Link between the effectiveness of ven-
i Monografie, 68. Wyd. UWM Olsztyn, 86 p. (in Polish).
dace management and stocking frequency – In:
Wo³os 1998a – General characteristics of coregonid manage-
Coregonid management. Conditions and effectiveness
ment in 132 Polish lakes – Arch. Pol. Fish. 6: 265-278.
(Eds) A. Wo³os, M. Bniñska, Wyd. IRS, Olsztyn: 23-28
Wo³os A. 1998b – Coregonid management and species suc-
cession – In: Coregonid management. Conditions and
Leopold M. 1998b – Vendace management effectiveness and
effectiveness (Eds) A. Wo³os, M. Bniñska, Wyd. IRS,
morphometric characteristics of lakes – In: Coregonid
management. Conditions and effectiveness (Eds) A.
Wo³os A., Mickiewicz M. 1998 – Characteristics of lakes and
Wo³os, M. Bniñska, Wyd. IRS, Olsztyn: 17-22 (in Polish).
management of vendace and whitefish – In: Coregonid
Mamcarz A., Skrzypczak A. 2002 – Coregonids in the Great
management. Conditions and effectiveness (Eds) A.
Masurian Lakes – In: Biology and Management of
Wo³os, M. Bniñska, Wyd. IRS, Olsztyn: 9-15.
Coregonid Fishes (Eds) T. Tood, G. Fleisher – Arch.Hydrobiol., Spec. Issues Advanc. Limnol. 57: 157-169.
Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).StreszczenieZastosowanie metody znakowanie – zwroty do oceny efektów zarybieñ jeziora Wigrylarwami sielawy, Coregonus albula (L.) w latach 2000-2001
W roku 2000 i 2001 przeprowadzono znakowanie w alizary-
naturalnego tar³a, jak i z zarybieñ, przyjmuj¹c podobn¹ prze-
nie S larw sielawy, Coregonus albula (L.), przeznaczonych do
¿ywalnoœæ ryb z obu Ÿróde³ rekrutacji. Stwierdzono, ¿e
zarybienia jeziora Wigry. Spoœród 19,2 mln larw sielawy
w od³owach sielaw z pokolenia 2000 ryby z zarybieñ stano-
w 2000 roku poznakowano 2 mln (10,4% ca³kowitej iloœci
wi³y 82,4%, a z pokolenia 2001 64,2% wszystkich od³owio-
wpuszczonych ryb) a w roku nastêpnym z 18,8 mln ryb, po-
nych osobników. Jezioro Wigry jest zbiornikiem o najwiêkszej
znakowano 7 mln (47,8%). W kolejnych latach od wszystkich
liczebnie populacji sielawy w Polsce, w którym co roku odby-
od³owionych sielaw pobierano otolity i ustalano ile z nich po-
wa siê jej masowe tar³o. Jednak wyniki opisywanych badañ
siada³o znaczek alizarynowy. Za³o¿ono, ¿e wszystkie osobniki
œwiadcz¹ o niezbêdnoœci systematycznych zarybieñ dla utrzy-
niepoznakowane pochodz¹, w równym stopniu, tak z

chapter: Monopoly 1. Each of the following firms possesses market power. Explain its source. a. Merck, the producer of the patented cholesterol-lowering drug Zetia b. WaterWorks, a provider of piped water c. Chiquita, a supplier of bananas and owner of most banana plantations d. The Walt Disney Company, the creators of Mickey Mouse Solution 1. a. Merck has a patent f